We present a theoretical analysis of the \(D^-\rightarrow \pi ^+\pi ^- \ell \bar{\nu }\) and \(\bar{D}^0\rightarrow \pi ^+\pi ^0 \ell \bar{\nu }\) decays. We construct a general angular distribution which can include arbitrary partial waves of \(\pi \pi \). Retaining the S-wave and P-wave contributions we study the branching ratios, forward–backward asymmetries and a few other observables. The P-wave contribution is dominated by \(\rho ^0\) resonance, and the S-wave contribution is analyzed using the unitarized chiral perturbation theory. The obtained branching fraction for \(D\rightarrow \rho \ell \nu \), at the order \(10^{-3}\), is consistent with the available experimental data. The S-wave contribution has a branching ratio at the order of \(10^{-4}\), and this prediction can be tested by experiments like BESIII and LHCb. Future measurements can also be used to examine the \(\pi \)–\(\pi \) scattering phase shift.